One type of a conventional apparatus for control of storing information into dial memories in a telephone set which is installed, for instance, in a car comprises a central processing unit (CPU), a read only memory (ROM) for storing a program, dial memories of a random access memory (RAM) having addresses designated by memory numbers, a key input unit for supplying the control unit with instruction by an operator, and a liquid crystal display (LCD) for displaying information stored in the dial memories.
In operation, when information such as a telephone number, a person's name, etc. is supplied from the key input unit to the control unit together with a memory number by an operator, an address of the dial memories designated by the memory number is accessed to check whether or not any information is stored in the addressed memory. If information is stored therein, the information is displayed on the LCD. Where the operator considers that the information may be erased, because it is not important, an erasing key provided on the key input unit is pressed on by the operator. Then, information supplied from the key input unit is written on the information stored in the addressed memory, so that the newly supplied information is stored in the addressed memory, while the formerly stored information is erased therefrom. On the other hand, where the operator considers the displayed information to be important, so that the operator does not want the stored information to be erased, the erasing key is not pressed on. Consequently, the important information is avoided from the erasing thereof.
Otherwise, when it is detected that no information is stored in the addressed memory, the newly supplied information is stored in that memory without any erasing key operation.
However, the conventional apparatus for control of storing information into dial memories in a telephone set has a disadvantage in that it is difficult to reliably avoid the erasing of important information, because erasing of any information (including writing of information on information to be erased) is carried out equally, regardless of the importance of stored information. In other words, information is written into dial memories equally, regardless of the importance of information to be stored. In order to surely avoid an erroneous erasing of important information, it is necessary that a memory number, by which a specific memory is designated to store important information, is always remembered. This is an additional disadvantage in the conventional apparatus for control of storing information into dial memories in a telephone set. In addition, even if the memory number is precisely remembered, the important information may be erased due to erroneous operation of a key on the key input unit. This is a further disadvantage.